Fluoroolefins represented by the formula: CF3(CX2)nCF═CH2, the formula: CF3(CX2)nCH═CHF, and the like are useful compounds as various functional materials, solvents, refrigerants, blowing agents, and monomers for functional polymers or starting materials of such monomers. For example, fluoroolefins are used as monomers for modifying ethylene-tetrafluoroethylene copolymers. In particular, of the fluoroolefins mentioned above, 2,3,3,3-tetrafluoropropene (HFO-1234yf) represented by CF3CF═CH2 has recently gained attention because it offers promising prospects as a refrigerant compound of low global-warming potential.
A known method for producing 2,3,3,3-tetrafluoropropene is a method in which halopropane or halopropene used as a starting material is fluorinated with hydrogen fluoride. For example, when 1,1,1,2,3-pentachloropropane (HCC-240db) used as a starting material is fluorinated in a gas phase, the reactions proceed in the route as described below.CCl3CHClCH2Cl+3HF→CF3CCl═CH2+4HCl  (1)CF3CCl═CH2+HF→CF3CF═CH2+HCl  (2)
In these reactions, the reaction rate in the reaction for producing 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf) from 1,1,1,2,3-pentachloropropane (first reaction) is significantly different from that in the reaction for producing 2,3,3,3-tetrafluoropropene from 2-chloro-3,3,3-trifluoropropene (second reaction). Thus, it is inefficient to perform these reactions using a single reactor, and it is ideal to perform the reactions using separate reactors.
Further, regarding the second reaction, i.e., the step of producing 2,3,3,3-tetrafluoropropene from 2-chloro-3,3,3-trifluoropropene, a method for producing 2,3,3,3-tetrafluoropropene in two reaction steps of adding hydrogen fluoride to 2-chloro-3,3,3-trifluoropropene, and then performing a dehydrochlorination reaction, is known.
For example, Patent Literature 1 listed below discloses a method in which fluorination is performed using halopropane or halopropene as a starting material in a gas phase in three steps under conditions according to each reaction, using three reactors containing different catalysts. Patent Literature 2 listed below discloses an integrated process using these reactions.
In these methods, however, it is difficult to obtain 100% conversion in the reaction of each step, and it is necessary to separate the unreacted starting materials and the target product from the reaction mixture to recycle the unreacted starting materials. Further, impurities, such as hydrogen chloride, contained in the reaction products tend to cause catalyst deterioration and a decrease in selectivity due to the occurrence of a side reaction in the next step. Thus, after the completion of each step, unwanted substances, such as hydrogen chloride, are generally removed from the reaction mixture using a distillation column, and components used as starting materials of the next step and the unreacted starting materials are separated. Regarding a method for producing 2,3,3,3-tetrafluoropropene using 1,1,1,2,3-pentachloropropane (HCC-240db) as a starting material in the two reaction steps described above, i.e., through the first reaction and the second reaction, FIG. 1 shows a flow diagram of a conventional typical treatment process. As shown in FIG. 1, the conventional method requires the following process: after the high-temperature reaction gases obtained in the first reaction, which contains 2-chloro-3,3,3-trifluoropropene, are cooled and HCl is removed in a purification step, the components are heated again to allow a reaction to proceed at a high temperature in the step of obtaining 2,3,3,3-tetrafluoropropene, and the gases obtained from the outlet of the second reaction step is cooled again to obtain the desired 2,3,3,3-tetrafluoropropene. Further, when unreacted 1,1,1,2,3-pentachloropropane and intermediates, such as 2-chloro-3,3,3-trifluoropropene, are recycled to the corresponding reaction steps, they must be reheated together with HF cooled in each purification step. As described above, the general production process, which requires repeated heating and cooling of the starting material gases, intermediates, products, and the like, results in significant energy loss and an increase in operating costs. The number of distillation columns required for separation is also increased, leading to an increase in equipment costs.